The 400 metres, or 400 metre dash, is a common sprinting event in track and field competitions. It has been featured in the athletics programme at the Summer Olympics since 1896 for men and since 1964 for women. On a standard outdoor running track, it is one lap around the track. Runners start in staggered positions and race in separate lanes for the entire course. In many countries, athletes previously competed in the 440 yard dash (402.336 m)—which is a quarter of a mile and was referred to as the 'quarter-mile'—instead of the 400 m (437.445 yards), though this distance is now obsolete. An athlete who competes in the 400 m may still be referred to as 'quarter-miler'; the distance or event might still be called the "quarter."
Maximum sprint speed capability is a significant contributing factor to success in the event, but athletes also require substantial speed endurance and the ability to cope well with high amounts of lactic acid to sustain a fast speed over a whole lap. While considered to be predominantly an anaerobic event, there is some aerobic involvement and the degree of aerobic training required for 400 metre athletes is open to debate.
The current men's world record is held by Wayde van Niekerk, with a time of 43.03 seconds; van Niekerk is also the reigning world and Olympic champion. The world indoor record holder is Kerron Clement, in 44.57 seconds. The current women's world record is held by Marita Koch, with a time of 47.60 seconds. Allyson Felix is the reigning women's world champion, while Shaunae Miller holds the women's Olympic title. The men's T43 (classification) Paralympic world record of 45.07 seconds is held by Oscar Pistorius.
An Olympic double of 200 metres and 400 m was first achieved by Valerie Brisco-Hooks in 1984, and later by Michael Johnson from the United States and Marie-José Pérec of France both in 1996. Alberto Juantorena of Cuba at the 1976 Summer Olympics became the first and so far the only athlete to win both the 400 m and 800 m Olympic titles.
The Olympic champion has frequently won a second gold medal in the 4 × 400 metres relay. This has been accomplished 14 times by men; Charles Reidpath, Ray Barbuti, Bill Carr, George Rhoden, Charles Jenkins, Otis Davis, Mike Larrabee, Lee Evans, Viktor Markin, Alonzo Babers, Steve Lewis, Quincy Watts, Jeremy Wariner and LaShawn Merritt; and 4 times by women; Monika Zehrt, Valerie Brisco-Hooks, Olga Bryzgina and Sanya Richards-Ross.
From 31 appearances in the Olympic Games, the men's gold medallist came from the USA 19 times.